Fire causes death, serious injury and significant material damages. The risk of fire can be reduced by using flame retardants effective in both, the solid and gas phase of the burning process.
Literature and practice show the availability of halogen containing flame retardants, which contain bromine or chlorine. They have proven effective for achieving the desired fire-protection effect in low application concentrations. The mechanism of their action is in the gas phase of the burning process, where H+ and OH− radicals are released from the burning gas in the flame burning phase, as a result of which the system is cooled-down and the formation of combustible gases and the release of heat are suppressed. During burning however, a major part of the halogen-containing flame retardants release halogen gases, harmful to human health and the environment.
In consideration of the protection of human health, as well as the environmental safety, now the phosphorus- and nitrogen-containing flame retardants are becoming widely used.
The phosphorus containing flame retardants, such as red phosphorus, phosphates, polyphosphates, organic phosphorus esters etc., are efficient in the solid phase of the burning process, where a charred layer is formed on material's surface, protecting it from the access of oxygen and heat that suppresses the formation and release of combustible gases, required for maintaining of the flame burning.
The nitrogen-containing flame retardants act, based on different mechanisms. Some of them form nitrogen netted structures in the treated material, which are relatively stable at high temperatures and prevent its decomposition and release of combustible gases. Other nitrogen-containing flame retardants release nitrogen as a gas, which dilutes the combustible gases, thus limiting the flame burning. The nitrogen-containing compounds display synergism with the phosphorus containing flame retardants by enhancing their effect.
There are many compositions of flame retardants, based on ammonium phosphates and methods for their production, described in the patent literature.
U.S. Pat. No. 3,900,327 illustrates a composition, which is a reaction product of the orthophosphoric acid or ammonium phosphate with ethylene oxide. It is known that the alkylene oxides, such as the ethylene oxide are toxic and carcinogenic, which makes the flame retardant practically unusable, although efficient as a flame retardant.
U.S. Pat. No. 6,989,113 describes a composition of a flame retardant, containing predominantly ammonium phosphate, urea, non-ionic surfactant, sugar and anti-foaming agent, which is used solely for fire protection of wooden surfaces.
As disclosed in RU2204582, the composition represents a dry-mixed composition of mono-, diammonium phosphate with urea and a surfactant. This fire-protection composition is used for treatment of cellulose-containing materials—wood, woven and non-woven fabrics, made of natural and mixed-type fibers, and paper.
Patent RU 2233296, as described in recent developments, is based on phosphorus- and nitrogen-containing components, as it does not only contain any halogen-containing compounds, but it also does not contain any surfactants either.
U.S. Pat. No. 5,064,710 outlines a composition that contains water solution of ammonium phosphate, an alkyl acid phosphate and a glycol, containing from 2 to 4 carbon atoms, which ensures reduced fume formation, during combustion of cardboard, when treated with the composition. However, this is only efficient for treatment of cellulosic materials, such as paper, plywood, fiber boards.
Patent BG 66022 (Patent application US 2008/138534 A1) describes a method of plasma chemical surface modification of porous materials and workpieces, where the treated materials are impregnated with the solution containing fire retardants according to BG 33508.
BG 33508 refers to a composition that ensures reduced combustibility of cotton textile materials. This formulation contains mainly orthophosphoric acid, urea, triethanolamine, ammonia water and optional surfactant-diisooctylsulphosuccinate, which is used solely for textile materials.
The main specific for the aforesaid compositions and the level of technique in this area, is that the efficiency of the known flame retardants is manifested selectively, with respect to certain types of polymers with various chemical structure.
In some fire-protection treatments, in case of swiftly changing humidity and high drying temperature of the impregnated materials there is an increased migration of the flame retardant towards the surface and unwanted depositions, which results in decreased fire-protection effect and deterioration of product's appearance.
A serious disadvantage for the fire protection of polymer materials by means of flame retardants is the trend for deterioration of their physical properties, such as loss of strength, which is a significant defect for certain materials such as fabrics, wooden materials, cardboard, leather and items, made of them.
Another shortcoming is the environmental safety of the ingredients of the flame retardants and the respective fire-protected polymers. The halogen-containing flame retardants are not safe, when being used, and in case of fire, they release toxic gases and smoke, which are very hazardous for human health, that could even cause death and serious injuries.
It is known that the toxic smoke is much more dangerous to people than the fire occurring as a result of ignition of polymer materials untreated with flame retardants. The U.S. Pat. No. 5,064,710 mentioned above, is the only example that provides data on smoke development tests of fire-protected cardboard.
There are not any compositions of flame retardants based on phosphorus- and nitrogen-compounds, known in the art, that could be applied to a wide range of porous hydrophilic and hydrophoblic polymers.